1. Field of the Invention
The present invention relates to fault restoration in a communication path or, in particular, to a system and a method for restoring a fault in a communication path, having a multiple layered structure, in a communication network.
2. Description of the Related Art
FIG. 1 shows an example of the configuration of a communication network, and FIG. 2 an example of a multiple layered structure of a communication path in this network.
As shown by (b) in FIG. 1, communication equipment of various transmission types such as SDH, PDH and those shown by (b) in FIG. 1 exist on the communication network. These equipment are connected to each other by communication paths of various transmission speeds. These communication paths, as shown by (c) in FIG. 1 and FIG. 2, have layers 5 to 7 based on a multiple layered structure (2M_SDH, 50M_SDH, 150M_SDH, etc.) of the communication path.
In recent years, the communication network has become so complicated that it is divided into a variety of domains including the access network, the basic network, the PDH network and the SDH network. As shown by (a) in FIG. 1, each domain is managed by subnetwork management systems (Sub-NMS) 2 to 4 for managing the internal cross connect devices. These management systems are further managed by a main network management system (Main-NMS) 1. The ITU-T Recommendation G. 805 appears to be able to manage of these complicated communication paths from the viewpoint of a layered structure.
Assume that a fault such as a disconnection occurs in a communication path 11 (communication path A) of 150 Mb/s on the 150M_SDH layer 5 as shown by X in FIG. 2. In the prior art, for early restoration from the fault, an alternative path 12, 13 for the particular communication path is formed using spare paths in the same layer 5. In the case where the restoration in the same layer is impossible, the fault is restored using lower-speed paths such as 50 Mb/s or 2 Mb/s in the layers 6, 7 on the client side accommodating the faulty path.
As described above, in the prior art, a fault in a communication path, if it occurs in a layer of high transmission speed, is restored first in the same layer, and therefore a high-speed spare path is required to be laid in all communication paths in advance. Even in the case where the communication path 11 before the fault covers only 10% of the whole band, therefore, a spare path of the same speed, i.e. 150 Mb/s is required for forming an alternative circuit.
Also, the spare path of 150 Mb/s, once assigned to a fault of the communication path having the utilization of only 10% described above, cannot be assigned to another fault, if any, of a communication path requiring 80% of the whole band which could otherwise have been assigned to the particular spare path.
As described above, the prior art has the problem that the efficiency of the spare capacity design against a communication path fault is very low.
In the case where a fault cannot be restored in the same layer as described above, the fault restoration is tried using a low-speed path included in the high-speed path. In such a case, the need of laying a spare path in the high-speed layer is eliminated, and therefore the design efficiency of the spare capacity is improved. In the prior art, however, many paths in the low-speed layer must be restored for reuse which consumes a vast amount of time to increase the adverse effect of the fault.
In view of these various problems, the object of the present invention is to provide a communication path fault restoration system and method for a communication network, with the operating conditions thereof under constant change as the communication paths open or close, in which a layer having an optimum communication path for fault restoration and the particular communication path are appropriately selected by use of a predetermined evaluation function. As a result, the spare capacity design efficiency against a communication path fault is conspicuously improved and rapid fault restoration is made possible.
According to the present invention, there is provided a communication path fault restoration system for communication network having a multiple layered communication path, comprising a communication path fault receiving unit for detecting a faulty path according to the network collection information, a communication path restoration select unit for selecting a communication layer to dynamically restore a faulty path thereon and a communication path on the particular communication path based on the result of determination of the information related to the faulty path according to a predetermined evaluation function, and a communication path restoration unit for performing the process of restoring the fault of the faulty path using the communication path on the selected communication layer.
The communication path restoration select unit repeats the determination based on the evaluation function for the selected communication layer, and thereby selects a communication layer requiring the fault restoration of the faulty path and a communication path on the particular layer. The evaluation function also selectively determines whether the fault restoration process is performed within the same layer as the faulty path or using the path of a different layer accommodating the faulty path.
The evaluation function makes the foregoing determination according to the traffic utilization rate of the faulty path. In the case where the utilization rate is not higher than a predetermined threshold level, the fault restoration process in the path of the layer on client side is selected. The utilization rate includes the ratio in which the contract band of the user represents the whole band and the peak cell rate of the ATM communication. Further, in the case where the number of the paths required to restore on client side is not less than a predetermined value, the selection on the client side is invalidated and the fault restoration process is performed in the same layer as the faulty path.
Also, the evaluation function selects the path on the server side when the number of faults occurring in a plurality of paths exceeds a predetermined value.
The communication path restoration select unit further includes an alternative path construction possibility information and, in the case where this alternative path construction possibility information is negative, the evaluation function selects another layer. The communication path restoration select unit further includes the priority information assigned to each path, and the evaluation function selects the processing of a communication path fault high in the priority order in the same layer.